The Syrian Democratic Forces (SDF) declared on Tuesday that they have completely recaptured the city of Raqqa from the ISIS terrorist organization.
"Everything is finished in Raqqa, our forces have taken full control of Raqqa," SDF spokesman Talal Sello told AFP.
A Reuters witness said fighting appeared to be almost at an end with only sporadic bursts of gunfire.
The US-backed SDF have seized control of the former ISIS stronghold, announced the Syrian Observatory for Human Rights later on Tuesday.
Victorious fighters celebrated in the streets, chanted slogans from their vehicles and raised a flag inside Raqqa stadium.
The SDF has been fighting ISIS inside Raqqa since June.
"We do still know there are still IEDs and booby traps in and amongst the areas that ISIS once held, so the SDF will continue to clear deliberately through areas," said Colonel Ryan Dillon, a spokesman for the US-led international coalition.
The four-month long battle for Raqqa left at least 3,250 people dead, more than a third of them civilians, the Observatory said.
In a sign that the battle for Raqqa was in its last stages, Dillon said there had been no coalition air strikes there on Monday.
ISIS also suffered setbacks Tuesday in the eastern Syrian region of Deir al-Zour, where Russian-backed regime forces retook swathes of territory, further reducing a "caliphate" that three years ago was roughly the size of Britain.
The Observatory said regime forces had brought the entire area stretching between Deir al-Zour and Mayadeen, which was retaken on Saturday, under their control following a major military offensive.
"These are not desert areas, they are villages along the Euphrates (river) that were ISIS strongholds," the Britain-based monitoring group said.
ISIS also controls territory in neighboring regions on the Iraqi side of the border, where they are facing another US-backed offensive by Iraqi pro-government forces.
ISIS has lost swathes of territory in Syria and Iraq this year, including its most prized possession, Mosul, and in Syria it has been forced back into a strip of the Euphrates valley and surrounding desert.